Previous techniques describe integrating low frequency antennas into mobile devices to provide for improved reception of FM radio and VHF and UHF analog and digital television. These techniques address the issues of embedding a low frequency into volume constrained communication devices, and also address the loading effects of the user as well as the structure and components in the mobile device. For cell phones in particular, it is important to consider all antennas in the device and develop a multi-antenna system to provide optimized communication performance at cellular bands as well as GPS, Bluetooth, FM, and other frequency bands.
More recently, near field communication (NFC) requirements have been placed on cell phone designers. NFC systems are becoming more popular, and are used in the retail community to provide a method of conducting financial transactions automatically and seamlessly. NFC is also being used to customize advertisements for individual consumers as well as providing a method of automating the process of registering and documenting coupons in the retail sector.
The difficulty involved in integrating NFC into a mobile device is the low frequency band assigned for this function. The 13.56 MHz frequency band is commonly used for NFC. The read distance, which is the distance that the NFC chipset in the mobile device can be interrogated by an NFC reader (transceiver) needs to be accurately controlled. If the read distance is too great the wrong consumer will be charged for a service during a transaction; if the read distance is too short, the transaction will not be conducted, resulting in a failure. To solve these problems (interrogation distance and frequency band of operation) an inductive coupling approach is taken in NFC system design, wherein two inductive coils, one attached to the NFC transceiver and the other attached to the NFC chipset in the mobile device couple when brought into close proximity. The coupled signal from the NFC reader is used to power the NFC chipset; the NFC chipset can then be commanded to transmit a coded signal back to the NFC reader using the inductive coupled link to complete the transaction.
With typical cell phones being volume constrained the difficulty of integrating an NFC antenna needs to be addressed by the handset design team. Ideally the NFC antenna could be designed an integrated into a mobile device wherein the NFC communication function as well as others communication functions can be serviced by the same radiating structure.